1. Field of the Invention
The present invention relates to a wafer dividing method of dividing a wafer into individual devices by a cutting blade cutting the wafer along streets, the wafer being formed with the devices sectioned by the streets, the devices being each formed of a laminated body in which an insulation film and a function film are laminated on the front surface of a semiconductor substrate.
2. Description of the Related Art
As well-known by those skilled in the art, a semiconductor device fabrication step forms a semiconductor wafer in which devices such as ICs, LSIs or the like formed in a matrix pattern by laminated bodies each formed of an insulating film and a function film laminated on the front surface of a semiconductor substrate such as silicon or the like. The semiconductor thus formed is sectioned by predetermined cutting lines called streets. Individual devices are manufactured by dividing the semiconductor wafer along the streets.
Such division of the wafer along the streets is generally executed by a cutting device. This cutting device includes a chuck table adapted to hold a semiconductor wafer, i.e., a workpiece; cutting means for cutting the semiconductor wafer held by the chuck table; and moving means for relatively moving the chuck table and the cutting means. The cutting means includes a rotary spindle rotated at high-speeds and a cutting blade attached to the spindle. The cutting blade is composed of a disklike base and an annular cutting edge attached to the lateral outer-circumferential portion of the base. The cutting edge is fixedly formed, by electrocasting, with e.g. diamond abrasive grains each having a diameter of about 3 μm.
In recent years, semiconductor wafers in the following form have been put to practical use in order to improve a throughput capacity for devices such as ICs, LSIs or the like. That is to say, the devices are each formed of a laminated body in which a low-dielectric insulation film (Low-k film) and a function film formed with a circuit are laminated on the front surface of a semiconductor substrate such as silicon or the like. The low-dielectric film is made of an inorganic film such as SiOF, BSG (SiOB) or the like or of an organic film which is a polymer film such as a polyimide-series, a parylene series or the like. Since the Low-k film mentioned above is different from the material of the wafer, it is difficult to cut both the Low-k film and the wafer at the same time by a cutting blade. More specifically, the Low-k film is very fragile like mica. Therefore, if the semiconductor wafer is cut along streets by the cutting blade, the Low-k film is exfoliated. The exfoliation reaches the circuit to pose a problem of fatally damaging the device.
To solve the problem mentioned above, a wafer dividing method is disclosed by Japanese Patent Laid-Open No. 2005-64231. In this method, a laminated body is sectioned by forming laser-processing grooves along respective streets formed on a semiconductor wafer. A cutting blade is positioned at each of the laser-processing grooves and the cutting blade and the semiconductor wafer are relatively moved. In this way, the semiconductor wafer is cut along the streets.
An energy distribution of a laser beam focused by a concentrator equipped with a generally used condenser lens exhibits a Gaussian distribution in which energy is strong at a central portion and is progressively weaker as it goes outward. Like this, the laser processing groove processed by the laser beam forming the Gaussian distribution causes unprocessed portions at lateral wall lower portions. It is necessary to form a laser processing groove having a width appropriately broader than the thickness of the cutting blade taking into account the unprocessed portions. This has to increase the interval between streets formed on the wafer. Thus, the streets account for a large portion of the wafer, posing a problem of poor productivity.